Field of the Invention
The present invention relates to an apparatus and method for measuring salinity of interstitial water collected from a soil sample. More particularly, the present invention relates to an apparatus and method for measuring salinity of interstitial water squeezed from a soil sample by performing the following steps: injecting a stream of high-pressure air into a plurality of soil-compressing tanks that contain the soil sample therein; collecting interstitial water, which is squeezed from the soil sample; measuring salinity of the interstitial water; and obtaining an average value of salinity, thereby enabling determination of engineering characteristics of the soil sample.
At least one of the soil-compressing tanks includes an upper filter assembly and a lower filter assembly, which are stacked sequentially and arranged horizontally or vertically, with a soil sample interposed between the upper filter assembly and the lower filter assembly. When the high-pressure air is supplied through an air nozzle into the soil-compressing tank in which the upper filter assembly, the soil sample, and the lower filter assembly are sequentially stacked, and a middle portion of the soil sample is pushed to create a fault line (also known as shear plane), causing shear stress. This enables not only measurement of the salinity of the interstitial water squeezed from the soil sample but also measurement of the shear strength of the soil sample.
The arrangement, in which at least any one of the soil-compressing tanks is horizontally or vertically arranged and in which the upper filter assembly and the lower filter assembly are sequentially arranged, with the soil sample interposed between the upper filter assembly and the lower filter assembly, also enables measurement of consolidation of the soil sample.
Description of the Related Art
Generally, soils collected from the seabed or a coastal area have different salinity. The salinity affects the engineering characteristics of collected soils.
That is, it is known that salinity affects the structure and arrangement of grains of soils. For example, salinity affects Atterberg limits.
Atterberg limits include the liquid limit and the plastic limit and are important factors in determining the consistency of soil. The liquid limit is defined as the critical water content at which the liquid state (behavior of soil) changes. For example, in the case of illite clay, when its salinity changes from 0 g/L to 30 g/L, its liquid limit also changes.
Even with a slight change in salinity, like from 0 g/L to 1 g/L, an increase in the liquid limit is observed.
Meanwhile, highly-swellable clay such as bentonite consisting mostly of montmorillonite tends to exhibit a dramatic decrease in the liquid limit when its salinity increases from 0 g/L to 30 g/L. Therefore, the liquid and plastic limits of soils change according to their salinity.
The consistency of soil is associated with unique shear strength (i.e., engineering characteristic), so the salinity of soil has a great impact on the geotechnical characteristic of soil. Moreover, salinity is also an important factor to be precisely measured for construction of buildings on saline soils, use of saline soils, prevention of disasters attributable to geological features of coastal areas, use of bentonite, and mobilization for submarine landslides.
For this reason, the demand for an apparatus which can extract salt from interstitial water collected from saline soils and measure the salinity of the interstitial water has grown.
To this end, Korean Patent Registration No. 10-0629320 (Patent Document 1), registered on Sep. 21, 2006, discloses an apparatus for measuring salinity using a differential salt sensor. The apparatus includes a differential salt sensor, a power supply means, and a housing. The differential salt sensor has a circuit in which four impedance elements Z1, Z2, Z3, and Z4 are connected in a diamond shape and in which opposite corners of the diamond-shaped circuit are connected to a power supply and a detector. When power is supplied to the terminal on the power supply side, the impedance relation “Z1Z2=Z3Z4” is establish and the potential difference at the terminal on the detector side becomes zero (0). Therefore, current does not flow, which means the current is in a balanced state. A reference seawater cylinder and a measurement seawater cylinder are connected in the form of a differential bridge to measure the electrical conductivity of reference seawater and measurement seawater. The salinity of the measurement seawater is measured using a difference in electrical conductivity between the reference seawater and the measurement seawater. The reference seawater cylinder includes an upper cover and a lower cover provided with respective electrode plates, with respective insulating plates interposed between the covers and the electrodes. The upper cover can move in the longitudinal direction of the cylinder. Similarly, the measurement seawater cylinder includes an upper cover and a lower cover provided with respective electrode plates, with respective insulating plates interposed between the covers and the electrodes. The measurement seawater cylinder has an opening in the sidewall so that seawater can be introduced into the measurement seawater cylinder. The power supply means supplies AC power to the differential salt sensor. The housing is a casing for encasing the differential salt sensor and the power supply means and has recesses in which the reference seawater cylinder and the measurement seawater cylinder are to be accommodated, respectively.
Korean Patent Registration No. 10-0441945 (Patent Document 2), registered on Jul. 16, 2004, discloses a salinity-measuring device including a digital conversion controller 10, a computer 30, a display/operation unit 20, a conductometric sensor 15, and a humidity sensor 16. The digital conversion controller 10 includes a current transformer 4 that measures current, an A/D converter 5 that converts the value of measured current output from the current transformer 4 into a digital signal, a Digital Signal Processor (DSP) 6 that receives and processes the digital signal output from the A/D converter 5, and a transmitter-receiver 7 that is connected to the DSP 6 to receive and transmit data. The computer 30 receives the signal output from the transmitter-receiver 7, and analyzes and stores the data. The display/operation unit 20 displays data after receiving the data from the DSP 6 through the transmitter-receiver 7, and enables an operation to change a measurement reference value. The conductometric sensor 15 is connected to one input terminal of the current transformer 4 and the humidity sensor 16 is connected to one input terminal of the A/D converter 5.
Despite existence of the related arts, there is still demand for improvement in an apparatus for measuring salinity of interstitial water squeezed from saline soils collected from a coastal area or a seabed and in a method for operating the apparatus.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.